Vibration buffering devices are conventionally known, for example, from Japanese Patent Application Laid-open Nos. 7-71526 and 5-180266.
The vibration buffering device disclosed in Japanese Patent Application Laid-open No. 7-71526 includes a plurality of first coil springs, and a plurality of second coil springs. The plurality of second coil springs are formed into an arcuate shape about the rotational axes of first and second mass members and are disposed outside the first coil springs in a radial direction of the mass members. It is required that an intermediate member, for operating the first and second coil springs having different operational radii in operative association with each other, bentegrated therewith since the load balance is lost if the intermediate member is divided. Hence, an increase in size cannot be avoided. If the distribution of end face loads of the first and second coil springs is taken into consideration, the intermediate member is obliged to be formed into a three-layer structure, resulting in an increase in number of parts. Moreover, a caulking pin or the like is required in order to provide the integrated three-layer structure, which also results in an increased number of parts and in a complicated assembling operation.
In the vibration buffering device disclosed in Japanese Patent Application Laid-open No. 5-180266, the first and second coil springs are disposed in series in an arcuate configuration about the rotational axes of the first and second mass members. The spring load of the second coil spring is set larger than that of the first coil spring. However, the weight of the second coil spring is relatively large. If a preload corresponding to the weight is not applied to the second coil spring, the second coil spring moves to produce a noise. However, since the first and second coil springs are connected in series, if a large preload is applied to the second coil spring, a preload applied to the first coil spring is also large, whereby the vibration buffering effect is degraded.